1. Technical Field
The invention relates to methods and apparatus for making three-dimensional (3D) shapes. More specifically, the invention relates to a method and apparatus for forming a 3D glass article.
2. Description of Related Art
Use of 3D glass covers for mobile display devices is on the rise. The glass covers are required to be highly precise in dimension and in the location of the 3D curvature relative to their outer peripheries. Typical dimensional tolerances are ±30 μm to ±50 μm. Consistent dimension is required for mounting the glass cover into a prescribed bevel in a display device without leaving unwanted, visible gaps between the bevel and glass cover. Centering of the contour of the glass cover relative to the display and touch screen is required for aesthetics and function.
The 3D glass cover can be made by thermally reforming a two-dimensional (2D) glass sheet into a 3D shape. To achieve the desired tolerances, such as those mentioned above, for some 3D shapes, it may be necessary to finish the edges of the 3D glass shape after the reforming process. However, edge-finishing requires precise alignment of the 3D glass shape on a computed numerically controlled (CNC) machine tool. A laser-based scanning vision system could be used to locate the center of the 3D glass shape, and the located center could then be used as a reference for alignment of the 3D glass shape on the CNC machine tool. However, laser-based scanning vision systems are costly, and scanning can be time consuming. The scanning of glass also requires specific lighting conditions since reflections such as those from a vacuum chuck used to hold the glass on the CNC machine tool can interfere with scanning For high-volume manufacturing, it is desirable to have a robust, low-cost setup that allows for the 3D glass shape to be positioned accurately and quickly in a repeatable manner on a CNC machine tool.
The alternative to thermally reforming a glass sheet into a 3D glass shape and then edge-finishing the 3D glass shape is to fully machine the 3D glass cover via a grind and polish process. This alternative concept has been industrialized in hand-held mobile devices such as media players. Because of the need to perform display-quality polishing to the ground glass surface and tool limitations for performing such polishing to the required quality, design options with this alternative approach are limited to shapes that can be made with a small amount of material removal and shapes with simplistic cylindrical and spherical convex shapes. However, industrial design groups for mobile devices desire glass cover surfaces with complex, non-cylindrical and non-spherical surfaces, which are not possible via a pure grind and polish process. This leaves the thermal reforming process as the more viable process for forming complex glass covers and the necessity to solve the problem of inadequate precision or difficulty in achieving a desired edge geometry associated with use of thermal reforming to make 3D shapes.